Washington, D.C. Suburb on high alert this evening. Authorities investigating a possible serial killer. Many neighbors rushing to install peepholes in their doors after what happened to one of their neighbors. ABC's Susan saulny is right there tonight. Reporter: It was a brazen crime in broad daylight. A beloved music teacher fatality shot after answering a knock at her front door in Alexandria, Virginia, late last week. The murder striking at the heart of a quaint community just outside Washington, D.C. People are kind of freaked out, because these things don't happen here. It's so sad, it's almost surreal. Reporter: The neighborhood was already on edge. Just three months ago, Ronald Kirby, a prominent local official, was gunned down inside his home by someone who entered without force. And the memory of the similar, unsolved murder in 2003 of Nancy Dunning, the wife of the late sheriff, is still raw. The three slayings happened within two miles of one another, leading residents to wonder whether a serial killer is on the loose. And now a manhunt is under way. Police released this sketch of a bearded man, suspected of the latest murder. Many people in this quiet community are scrambling now to install peepholes in their front doors, so they can spot the suspect, should he try to strike again. We're going to do everything we can to catch whomever did this. Reporter: Police say they have no motive and city leaders are urging residents to remain calm, and on alert.

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